Insulator having excellent arc resistance

ABSTRACT

A highly heat-resistant fluororesin, such as tetrafluoroethylene resin or tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, is filled with 0.5 to 1 weight % of a non-black insulating pigment that has a heat resistance such that discoloration does not occur when the fluororesin is baked. Green insulating pigment whose main component is a TiO 2 —CoO—NiO—ZnO system or a ZnO—CoO system, or blue insulating pigment whose main component is a CoO—Al 2 O 3  system or a CoO—Al 2 O 3 —Cr 2 O 3  system is used singly or in a combination, as the non-black insulating pigment. A highly arc-resistant insulator is provided that secures an insulating capacity and at the same time that secures an excellent ability to prevent both interior and exterior deterioration of the insulator and that avoids color heterogeneity and localized discoloration.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Divisional of U.S. application Ser. No.12/064,798, filed Jun. 19, 2008, which is a National Stage Applicationof PCT No. PCT/JP2006/316759 filed Aug. 25, 2006, and claims the benefitof priority from prior Japanese Patent Application No. 2005-246640,filed Aug. 26, 2005, the entire contents of each of these applicationsare incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a highly arc-resistant insulator and inparticular relates to a highly arc-resistant insulator that is suitablefor use in, for example, circuit breakers in which arcing is generatedbetween electrodes.

BACKGROUND ART

In the case of devices in which arcing is generated between electrodesin the device, an insulator is disposed in the vicinity of the arcing inorder to protect the other parts of the device from the heat andultraviolet-rich light from the arcs. These devices can be exemplifiedby circuit breakers in which arcing is extinguished by spraying sulfurhexafluoride gas (SF₆ gas) between the electrodes and arc chute breakersin which a magnetic field is applied by coils disposed on both sides ofthe electrodes and arcing is extinguished by blowing sulfur hexafluoridegas into a region known as the arc chute.

Fluororesin not filled with another substance was used for thisprotective insulation in the past. However, when an unfilled fluororesinwas used, the heat and ultraviolet-rich light from the arcing generatedduring circuit interruption produced an electrically conductivecarbonized material not just on the surface of the resin, but also inthe interior of the resin, causing a substantial reduction in theinsulating performance.

In addition, gas generated by the resin's interior carbonization wasdischarged from the interior, causing ejection of the fluororesin. Thisresulted in the formation of substantial unevenness in the surface ofthe resin and a substantial decline in the mechanical strength of theinsulator disposed for purposes of protection. Another problem was thatthe unevenness formed in the resin's surface resulted in a poor gas flowwhen the arc-extinguishing gas was blown in and prevented an adequatecooling effect from being obtained.

In response to these problems, Patent Document 1 proposes that thefluororesin be filled with boron nitride; this reflects the light fromthe arc and prevents its penetration into the interior of the resin andthereby prevents interior deterioration. Due to its filling with boronnitride, this insulator is whiter than the unfilled insulator and alsohas a higher light reflectance. However, a punctiform discoloration andcolor heterogeneity not seen for the boron nitride-free fluororesin byitself have been produced in some instances due, inter alia, to fillingwith a mixture of boron nitrides from different production lots and theresidence in the resin of gas produced from the boron nitride duringresin baking.

These discolored regions absorb heat and ultraviolet radiation from thearcing more readily than other regions, which, being white, have ahigher reflectance, and this can cause local deterioration. Since as aconsequence it must basically be ensured that an insulator that exhibitssubstantial color heterogeneity and/or regions of discoloration is notused, quality control becomes more problematic than for an insulator notfilled with boron nitride, which drives up the cost of quality controland makes it difficult to improve production efficiency.

In addition, while materials obtained by loading a fluororesin with 10to 20 weight % of boron nitride have entered into widespread use at thepresent time as insulators for circuit breaking applications, sinceboron nitride has a high thermal conductivity fluororesin loaded with 10to 20% boron nitride ends up having a high thermal conductivity, whichhas led to the additional problem of an elevated heat-induced wear ofthe fluororesin.

The addition of molybdenum disulfide MoS₂ is proposed in Patent Document2 in order to absorb the heat and ultraviolet-rich light from the arcingin the surface layer and thereby prevent interior deterioration. Thismethod can almost entirely eliminate color heterogeneity anddiscoloration due to its blackening effect. However, both MoS₂ andcarbon, which is widely used as a black pigment, are electroconductivematerials, and as a consequence the insulating performance of theinsulator and its arc resistance are reduced even when the filling rateis controlled.

The addition of 0.2 to 5 weight % of an inorganic pigment having aparticle diameter no greater than 1 μm and/or organic pigment having aparticle diameter of 0.5 μm is proposed in Patent Document 3. However,there is no stipulation of the resin/pigment combination, and thetechnology shown in Patent Document 3 (for example, filling apolytetrafluoroethylene resin, which requires baking at around 300° C.,with an organic pigment having a heat resistance of only hundred andseveral tens degrees centigrade and/or with ultramarine blue pigment,which gradually discolors at temperatures of 300° C. and above, istaught therein) cannot solve the problem of color heterogeneity anddiscoloration, which is one of the problems that the present inventionis directed to solving.

-   Patent Document 1: Japanese Patent Publication No. H1-37822-   Patent Document 2: Japanese Patent Application Laid-open No.    H10-172400-   Patent Document 3: Japanese Patent Publication No. 562-60783-   Non-Patent Document 1: “Colorant Engineering Handbook”, Japan    Society of Color Material, Asakura Publishing Co., Ltd., 1989

DISCLOSURE OF THE INVENTION

As described above, it has not been possible with the insulatorsheretofore used in, for example, circuit breakers, to prevent a declinein insulating performance and/or a decline in arc resistance, nor has itbeen possible to prevent the generation of color heterogeneity anddiscoloration.

The present invention was pursued in order to solve these problems andhas as an object the introduction, based on maintaining the insulationperformance while preventing color heterogeneity and localizeddiscoloration and securing a satisfactory capacity to prevent bothinterior and exterior of deterioration of the insulator, of a highlyarc-resistant insulator that enables an improved consistency in productquality.

In order to achieve the aforementioned object, the highly arc-resistantinsulator of one aspect of the present invention is an insulator that isdisposed and used in the vicinity of arcing that is generated betweenelectrodes, the insulator comprising a prescribed fluororesin filledwith 0.5 to 1 weight % of a non-black insulating pigment that has a heatresistance such that discoloration does not occur when the fluororesinis baked, and the insulator is characterized in that the fluororesin isa polytetrafluoroethylene resin or a tetrafluoroethylene-perfluoroalkylvinyl ether copolymer, and a pigment whose main component is either aTiO₂—CoO—NiO—ZnO system green insulating pigment, or a CoO—Al₂O₃—Cr₂O₃system blue insulating pigment is used singly or in combination, as thenon-black insulating pigment.

The highly arc-resistant insulator in another aspect of the presentinvention is an insulator that is disposed and used in the vicinity ofarcing that is generated between electrodes, the insulator comprising aprescribed fluororesin filled with 0.05 to 0.2 weight % of a blackinsulating pigment that has a heat resistance such that discolorationdoes not occur when the fluororesin is baked, and the insulator ischaracterized in that the fluororesin is a polytetrafluoroethylene resinor a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer; and apigment whose main component is any of a CuO—Cr₂O₃ system, aCoO—Cr₂O₃—Mn₂O₃ system, a CoO—Fe₂O₃—Cr₂O₃ system, or a CuO—Fe₂O₃—Mn₂O₃system, is used, singly or in a combination, as the black insulatingpigment.

In order to achieve the aforementioned object, the highly arc-resistantinsulator of one aspect of the present invention is an insulator that isdisposed and used in the vicinity of arcing that is generated betweenelectrodes, the insulator comprising a prescribed fluororesin filledwith 0.5 to 1 weight % of a non-black insulating pigment that has a heatresistance such that discoloration does not occur when the fluororesinis baked.

The highly arc-resistant insulator in another aspect of the presentinvention is an insulator that is disposed and used in the vicinity ofarcing that is generated between electrodes, the insulator comprising aprescribed fluororesin filled with 0.05 to 0.2 weight % of a blackinsulating pigment that has a heat resistance such that discolorationdoes not occur when the fluororesin is baked.

The reduction in insulating performance caused by interior carbonizationof the fluororesin can be prevented in an insulator having thecharacteristic features cited above through the absorption of thedamaging light by the insulating pigment that has been introduced invery small amounts. In addition, because the thermal conductivity doesnot become elevated in this insulator, heat- and light-inducedfluororesin wear can be reduced. Moreover, quality control can be madeeasy, quality control costs can be reduced and production efficiency canbe improved because, through filling with a black or other coloredpigment that absorbs the damaging light, substantial color heterogeneityand local discoloration can also be inhibited more effectively than whenthe insulator is whitened by filling with boron nitride. An improvedconsistency in product quality is thereby made possible. Furthermore, ahigh mechanical strength can be maintained since the insulating pigmentis introduced at very low filling rates.

The present invention, by maintaining the insulation performance whilepreventing color heterogeneity and localized discoloration and securinga satisfactory capacity to prevent both interior and exteriordeterioration of the insulator, can provide a highly arc-resistantinsulator that enables an improved consistency in product quality.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross section that shows the structure of a firstembodiment of the highly arc-resistant insulator according to thepresent invention;

FIG. 2 shows the relationship between the filling rate and the averagelight absorptivity for the use of the non-black insulating pigment;

FIG. 3 is a schematic cross section that shows the structure of a secondembodiment of the highly arc-resistant insulator according to thepresent invention;

FIG. 4 shows the relationship between the filling rate and the averagelight absorptivity for the use of the black insulating pigment;

FIG. 5 is a graphical representation of the relationship between theabsorbance area in the 500 to 550 nm wavelength region and the nozzlethroat diameter wear rate for the examples shown in Tables 3 and 4;

FIG. 6 is a graphical representation of the relationship between theabsorbance area in the 500 to 550 nm wavelength region and the weightwear rate for the examples shown in Tables 3 and 4;

FIG. 7 shows the light absorption spectra for the examples shown inTables 3 and 4; and

FIG. 8 shows the light reflection spectra for the examples shown inTables 3 and 4.

EXPLANATION OF REFERENCE LETTERS

-   1: FLUORORESIN-   2: NON-BLACK INSULATING PIGMENT-   3: LIGHT FROM ARC-   4: ARC-   10: BLACK INSULATING PIGMENT

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments that apply the present invention are specifically describedherebelow with reference to the drawings.

(1) First Embodiment (1-1) Structure

As shown in FIG. 1, the highly arc-resistant insulator of thisembodiment comprises a fluororesin 1 filled with a non-black,chemical-resistant insulating pigment 2 that has a heat resistance suchthat discoloration does not occur when the fluororesin is baked.

(Fluororesin)

The use of polytetrafluoroethylene resin andtetrafluoroethylene-perfluoroalkyl vinyl ether copolymer for thefluororesin 1 is particularly preferred. This is becausepolytetrafluoroethylene resin, with its melting point of about 327° C.,and tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, with itsmelting point of about 302 to 310° C., have a high heat resistance evenamong the fluororesins.

Due to its high melt viscosity, polytetrafluoroethylene resin ischaracterized by an ability to maintain its original shape even whenmelted at high temperature. By positioning the highly arc-resistantinsulator of this embodiment while maintaining a suitable distance fromthe arcing, this property can be exploited to prevent heat-induceddistortion even when arc-induced heating occurs.

Moreover, both the aforementioned polytetrafluoroethylene resin andtetrafluoroethylene-perfluoroalkyl vinyl ether copolymer are convertedby thermal degradation into the unit constituent molecules that comprisethe polymer and are thereby converted into a gas; as a consequence,there is no residual carbonized material. This accrues the advantage ofinhibiting the decline in insulating performance that is induced by theproduction of electroconductive material. In addition, a cooling effectis developed due to the large amount of energy consumed duringdegradative gasification, which has the additional effect of protectingthe polytetrafluoroethylene resin itself or thetetrafluoroethylene-perfluoroalkyl vinyl ether copolymer itself.

(Non-Black Insulating Pigment)

The fluororesin 1 is filled with a non-black, chemical-resistantinsulating pigment 2 that has a heat resistance such that discolorationdoes not occur when the fluororesin 1 is baked. This insulating pigment2 inhibits the formation of carbonized material in the resin's interiorby absorbing, from the light 3 produced from the arc 4, mainly light inthe wavelength region that participates in interior deterioration andinhibits a reduction in insulating performance by preventing thefluororesin ejection induced by gas produced in the interior.

Thus, when filling is carried out using an electroconductive substancesuch as carbon, even at a low filling rate, for example, the insulationresistance of the fluororesin 1 is reduced and the adjacent arc caneasily flow across the surface of the electroconductive material-filledfluororesin 1, and the arc resistance thus ends up being reduced. Incontrast to this, when filling with the non-black insulating pigment 2used in this embodiment is employed, there is no reduction in theinsulation resistance of the fluororesin 1 and a highly arc-resistantinsulating material can be obtained as a result.

The non-black insulating pigment 2 used in this embodiment is preferablya non-black insulating pigment 2 that has a heat resistance such thatneither deformation nor discoloration occurs at around 300° C., which isthe baking temperature for the fluororesin 1, and that has a chemicalresistance such that the pigment is not attacked by thefluorine-containing gases generated from the fluororesin 1 pre-baking.The use of pigment lacking heat resistance or chemical resistance leadsto a reduced insulating performance just as for the addition ofelectroconductive pigment, due to the generation of discoloration whenthe fluororesin is baked or the production of carbonized material.

(Specific Examples of the Non-Black Insulating Pigment)

The following are effective for blocking the light from the arc andreducing the light absorption-induced wear of insulator, vide supra:rationalizing the filling rate of the non-black insulating pigment 2, asdescribed below, and adjusting the wavelength region of the lightabsorbed by the non-black insulating pigment 2. Thus, the reasoning isthat if mainly light in the wavelength region involved with interiorcarbonization were to be absorbed and light outside this wavelengthregion were not to be absorbed, then a highly arc-resistant insulatorcould be obtained that would accrue both of the following effects: aninhibition of a reduction in insulating performance induced by interiorcarbonization and a reduction in the light- and heat-induced wear of thefluororesin 1.

As a result of intensive and extensive investigations by the presentinventors from this point of view, it was discovered that the use,singly or in a combination, of green pigment or blue pigment yields ahighly arc-resistant insulator free of color heterogeneity and so forthand accrues both of the following effects: an inhibition of a reductionin insulating performance induced by interior carbonization and areduction in the light- and heat-induced wear of the fluororesin 1.

The green color cited herein denotes the region comprising GY, G, and BGamong the 10 principal hues in the Munsell wheel (hue) of the Munsellcolor system, while the blue color cited herein denotes the regioncomprising BG, B, and PB among the 10 principal hues of the Munsellwheel of the Munsell color system.

More specifically, pigment whose main component is a TiO₂—CoO—NiO—ZnOsystem or a ZnO—CoO system is preferably used as the green inorganicpigment and pigment whose main component is a CoO—Al₂O₃ system or aCoO—Al₂O₃—Cr₂O₃ system is preferably used as the blue inorganic pigment.These pigments are insulating pigments that exhibit an excellent heatresistance and an excellent chemical resistance and that when filledinto the fluororesin 1 do not undergo distortion or discoloration whenheated during baking.

Moreover, as noted above, the light- and heat-induced wear of thefluororesin 1 can be kept low by inhibiting interior carbonizationthrough the effective absorption of the light that participates ininterior deterioration and by not absorbing light other than that.

(Filling Rate for the Non-Black Insulating Pigment)

The filling rate for the non-black insulating pigment in the fluororesinwill now be considered. Viewed from the perspective of countering colorheterogeneity and discoloration in the highly arc-resistant insulator ofthis embodiment, there exists a color density sufficient for effectivelypreventing color heterogeneity and discoloration, that is, there existsa minimum filling rate. However, when the non-black insulating pigment 2is introduced in large amounts, the light 3 from the arc is absorbed inlarge amounts and its conversion into thermal energy then producesthermal degradation and thermal deterioration. This results in anincrease in the wear of the insulator comprising the fluororesin 1. Anappropriate color and amount must therefore be set for the addedpigment.

A typical relationship is shown graphically in FIG. 2 between thefilling rate and the average light absorptivity for fluororesin 1 filledwith non-black insulating pigment 2. This average light absorptivity isthe average value over the measured wavelength region of theabsorptivity in the light absorption spectrum determined from the lightreflection spectrum measured on the fluororesin 1 filled with non-blackinsulating pigment 2. As shown in FIG. 2, the average light absorptivityincreases with increasing filling rate in a filling rate range of 0.1 to1 weight % of the insulating pigment 2, and remains almost unchanged ata filling rate greater than 1 weight %.

As noted previously, an unnecessary increase in light absorption is acause of thermal degradation and thermal deterioration and is thusassociated with an increase in the amount of wear of the insulatoritself. Accordingly, with regard to the filling of the non-blackinsulating pigment 2 into the fluororesin 1, a filling rate no greaterthan 1 weight % is sufficient. On the other hand, according to theresults of investigations by the present inventors, color heterogeneityand punctiform discoloration could not be prevented when the fillingrate fell below 0.5 weight % (approximately 70% for the average lightabsorptivity). As a consequence, a filling rate of at least 0.5 weight %but no more than 1 weight % is preferred when the fluororesin 1 isfilled with a non-black insulating pigment 2.

(1-2) Function and Effect

This embodiment, through the absorption by the non-black insulatingpigment 2 filled at very small levels in the fluororesin 1 mainly of thelight in the wavelength region that participates in interiordeterioration (i.e., damaging light), can prevent a reduction ininsulation performance by inhibiting the formation of carbonizedmaterial within the resin and preventing ejection of the fluororesin bygas produced in the interior.

In addition, because the non-black insulating pigment 2 used in thisembodiment does not absorb much light outside the wavelength region thatparticipates in interior deterioration, the degradation, gasification,and dissipation of resin from the insulator surface that is produced bylight and heat absorption does not become unnecessarily large. As aresult, decrease (wear) of the insulator as a whole can also beinhibited while achieving the suppression of interior deterioration.Since the filling rate with the non-black insulating pigment 2 is verylow in this embodiment, the increase in thermal conductivity seen infilling with a substance that has a high thermal conductivity, such asboron nitride, also does not occur. This enables a reduction in thelight- and heat-induced wear of the fluororesin.

In addition, since the aforementioned fluororesin is uniformly coloredby the uniformly dispersed non-black insulating pigment 2, this canprevent, for example, the color heterogeneity and punctiformdiscoloration that can be generated when a white filler, such as boronnitride, is used. From the perspective of quality management, the resultof this is that there will be little insulator that due to the presenceof color heterogeneity or punctiform discoloration cannot be used inactual devices, which in turn enables facile quality control, areduction in quality control costs, and an improve in productiveefficiency. An improved consistency in product quality can therefore beenvisaged. A high mechanical strength can also be maintained since thefilling rate with the insulating pigment is very low.

(2) Second Embodiment

This embodiment uses a black pigment, which absorbs light over theentire wavelength range, as the pigment filled into the fluororesin 1.In this case also, just as for the first embodiment described in thepreceding, the appropriate selection of the filling rate yields a highlyarc-resistant insulator free of color heterogeneity and accrues both ofthe following effects: an inhibition of the reduction in insulatingperformance induced by interior carbonization and a reduction in thelight- and heat-induced wear of the fluororesin 1.

(2-1) Structure

The highly arc-resistant insulator of this embodiment, as shown in FIG.3, comprises a fluororesin 1 filled with a black, chemical-resistantinsulating pigment 10 that absorbs light over the entire wavelengthregion and that has a heat resistance such that discoloration does notoccur when the fluororesin is baked. Again as for the first embodimentdescribed above, polytetrafluoroethylene resin ortetrafluoroethylene-perfluoroalkyl vinyl ether copolymer is preferablyused as the fluororesin. The reason for this is the same as above andwill therefore not be described again.

(Black Insulating Pigment)

For example, pigment in which the main component is the CuO—Cr₂O₃system, CoO—Cr₂O₃—Mn₂O₃ system, CoO—Fe₂O₃—Cr₂O₃ system, orCuO—Fe₂O₃—Mn₂O₃ system is preferably used, singly or in a combination,as the black, chemical-resistant insulating pigment 10 that has a heatresistance such that discoloration does not occur when the fluororesinis baked. These pigments are insulating pigments that have an excellentheat resistance and an excellent chemical resistance and can preventdeterioration by effectively absorbing the light that participates ininterior deterioration.

(Filling Rate for Black Insulating Pigment)

The filling rate for the black insulating pigment in the fluororesinwill now be considered.

A typical relationship is shown in FIG. 4 between the filling rate andthe average light absorptivity for fluororesin 1 filled with blackinsulating pigment 10. This average light absorptivity is the averagevalue over the measured wavelength region of the absorptivity in thelight absorption spectrum determined from the light reflection spectrummeasured on the fluororesin 1 filled with the black insulating pigment.

As shown in FIG. 4, the average light absorptivity increases withincreasing filling rate in a filling rate range for the black insulatingpigment 10 of 0.05 to 0.2 weight % and remains almost unchanged at afilling rate greater than 0.2 weight %. As noted previously, anunnecessary increase in light absorption is a cause of thermaldegradation•thermal deterioration and is thus associated with anincrease in the amount of wear of the insulator itself. Accordingly,with regard to the filling of the black insulating pigment 10 into thefluororesin 1, a filling rate no greater than 0.2 weight % issufficient.

On the other hand, according to the results of investigations by thepresent inventors, color heterogeneity and punctiform discolorationcould not be prevented when the filling rate fell below 0.05 weight %(approximately 70% for the average light absorptivity). As aconsequence, a filling rate of at least 0.05 weight % but no more than0.2 weight % is preferred when the fluororesin 1 is filled with a blackinsulating pigment 10.

(2-2) Function and Effect

The black insulating pigment 10 used in this embodiment, while absorbinglight over the entire wavelength range, has an extremely small fillingrate of at least 0.05 weight % but not more than 0.2 weight %, and thismakes it possible to prevent unnecessary light absorption. Because ofthis, the degradation, gasification, and dissipation of resin from theinsulator surface can be prevented and, as a result, decrease (wear) ofthe insulator as a whole can also be inhibited while achieving thesuppression of interior deterioration. Since the filling rate with theblack insulating pigment 10 is extremely low in this embodiment, theincrease in thermal conductivity seen in filling with a substance thathas a high thermal conductivity, such as boron nitride, also does notoccur. This enables a reduction in the light- and heat-induced wear ofthe fluororesin.

In addition, since the aforementioned fluororesin is uniformly coloredby the uniformly dispersed black insulating pigment 10, this canprevent, for example, the color heterogeneity and punctiformdiscoloration that are generated when a white filler, such as boronnitride, is used. From the perspective of quality management, the resultof this is that there will be little insulator that due to the presenceof color heterogeneity or punctiform discoloration cannot be used inactual devices, which in turn enables facile quality control, areduction in quality control costs, and an improve in productiveefficiency. An improved consistency in product quality can therefore beenvisaged. A high mechanical strength can also be maintained since thefilling rate for the insulating pigment is very low.

(3) Third Embodiment

This embodiment concerns an investigation into the optimal value of theparticle size of the non-black insulating pigment 2 or black insulatingpigment 10 to be filled in the fluororesin 1.

Evaluation parameters are available for each of the pigments describedabove, i.e., the “hiding power”, which denotes the capacity to cover orobliterate the underlying surface when filling with a pigment is carriedout, and the “tinting strength”, which is the coloring capacity for theaddition of a prescribed amount of pigment. The “hiding power” isdetermined by the light reflected by the surface of the pigmentparticles and the light absorbed by the pigment, and larger amounts ofreflected light and absorbed light provide a higher hiding power. Thehiding power is also related to the particle size of the pigmentparticles, and it is known that at small particle sizes, for example, atparticle diameters less than or equal to one-half the wavelength of thelight, the hiding power generally undergoes a substantial decline due tolight scattering and diffraction phenomena that are different fromreflection and refraction (refer, for example, to Non-Patent Document1). Since the present invention is focused on the UV-visible region andthe maximum wavelength for this region is 800 nm, at a minimum it isthen necessary to make the particle size of the insulating pigment 400nm (0.4 μm) or more in order to efficiently absorb light in this region.

With regard to the “tinting strength”, on the other hand, smallerparticle sizes provide a stronger tinting strength and the tintingstrength tends to decline as the size increases. It can therefore beconcluded with regard to the particle size that there is an upper limitat which the minimum required tinting strength can be exhibited. Theresults of extensive investigations at different particle sizes showedthat an excellent hiding capacity and an excellent tinting strength canbe obtained for the insulating pigment of the present invention when theaverage particle size is between 0.4 and 2 μm.

Moreover, it was found that, when the fluororesin 1 is filled at thefilling rate cited above with green, blue, or black insulating pigmentwithin this particle size range, the absorptivity from the arc-generatedlight 3 of light that participates in interior deterioration and thetransmissivity for light that when absorbed is converted to thermalenergy and causes insulator wear, are balanced, making it possible toobtain a highly arc-resistant insulator in which interior deteriorationdoes not occur and for which there is also little wear. It wasadditionally found that the manifestation of color heterogeneity anddiscoloration could also be prevented due to the generation of asatisfactory coloration.

EXAMPLES

Specific examples are provided below.

The results of an investigation of the properties, e.g., volumeresistivity, arc resistance, and so forth, of fluororesins filled withdifferent insulating pigments are shown in Table 1. Examples 1 to 4 areexamples according to the present invention, wherein Examples 1 and 2concern filling with a green insulating pigment, Example 3 concernsfilling with a blue insulating pigment, and Example 4 concerns fillingwith a black insulating pigment. Comparative Example 1 concerns fillingwith carbon, an electroconductive material, while Comparative Example 2concerns unfilled tetrafluoroethylene resin (PTFE). The arc resistancetest was in accordance with the method described in JIS K 6911.

TABLE 1 volume arc filling rate resistivity resistance filler colorresin (weight %) (Ω · cm) (seconds) Example 1 TiO₂—CoO—NiO—ZnO greentetrafluoroethylene- 0.7 1 × 10¹⁷ ≧270 system perfluoroalkyl vinyl ethercopolymer Example 2 TiO₂—CoO—NiO—ZnO green tetrafluoroethylene 0.7 2 ×10¹⁷ ≧270 system Example 3 CoO—Al₂O₃—Cr₂O₃ blue tetrafluoroethylene 0.72 × 10¹⁷ ≧270 system Example 4 CuO—Cr₂O₃ system blacktetrafluoroethylene 0.4 2 × 10¹⁷ ≧270 Comparative carbontetrafluoroethylene 0.4 2 × 10¹² 180 Example 1 Comparative nonetetrafluoroethylene 0 1 × 10¹⁸ ≧270 Example 2

As is clear from Table 1, the volume resistivity and arc resistance weresubstantially reduced when an electroconductive material (carbon) wasfilled, as shown in Comparative Example 1. In contrast to this, whenfilling was carried out using an insulating inorganic pigment accordingto the present invention, as in Examples 1 to 4, a high volumeresistivity was obtained while the arc resistance could also bemaintained at the same level as for the unfilled tetrafluoroethyleneresin (PTFE) that was the subject of Comparative Example 2.

The results of an investigation of the presence/absence of interiordeterioration during exposure to arc light and the weight wear duringthis exposure are shown in Table 2 for tetrafluoroethylene resin (PTFE)filled with different insulating pigments. Examples 11 to 18 areexamples according to the present invention, wherein Examples 11 to 13concern filling with a green insulating pigment, Examples 14 and 15concern filling with a blue insulating pigment, and Examples 16 to 18concern filling with a black insulating pigment. Comparative Example 11concerns unfilled tetrafluoroethylene resin (PTFE). The “weight wear” isreported as a relative value where 100 is assigned to the weight wearper unit energy of the tetrafluoroethylene resin (PTFE) not filled withinsulating resin, which is the subject of Comparative Example 11.

TABLE 2 presence/absence of filling rate particle interior filler color(weight %) size (μm) carbonization tracks wear Example 11TiO₂—CoO—NiO—ZnO green 0.5 0.01 present 100 system (small number)Example 12 TiO₂—CoO—NiO—ZnO green 0.5 1.3 absent 100 system Example 13ZnO—CoO system green 1.0 0.6 absent 150 Example 14 CoO—Al₂O₃ system blue0.5 0.6 absent 110 Example 15 CoO—Al₂O₃—Cr₂O₃ blue 0.5 0.6 absent 110system Example 16 CuO—Cr₂O₃ system black 0.2 0.6 absent 250 Example 17CuO—Cr₂O₃ system black 0.07 0.6 absent 130 Example 18 CoO—Cr₂O₃—Mn₂O₃black 0.1 0.3 present 150 system (small number) Comparative none 0 —present 100 Example 11 (large number)

As is made clear from Table 2, when, for the case of filling with anon-black insulating pigment (Examples 11 to 15), the filling rate wasaround 0.5 weight % and the average particle size was in the range of0.4 to 2 μm, interior carbonization and the associatedtetrafluoroethylene resin erosion did not occur, while the wear could bebrought to about that of the system, provided as Comparative Example 11,not filled with insulating pigment. In addition, interior carbonizationtracks were seen in Example 11, where the particle size was small at“0.01 μm”, and the wear was high at “150” in Example 13, where thefilling rate was high at “1.0”.

Upon comparing the results from Examples 16 and 17, which used the sameblack insulating pigment at a filling rate of “0.2” and “0.07”,respectively, Example 16 had a high wear of “250”. It may be understoodfrom this that a rationalization of the filling rate for filling with ablack insulating pigment makes it possible to also bring down the amountof wear while inhibiting interior carbonization. On the other hand,interior carbonization tracks were seen in Example 18, in which theparticle size was small at “0.3” μm.

As is clear from the preceding results, the highly arc-resistantinsulator of the present invention, by filling a fluororesin with asuitable amount of an appropriate insulating pigment, can avoid theinterior carbonization caused by the arc light while, by avoiding theabsorption of excess light and heat from the arc, can also suppressinsulator wear. In addition, by suppressing color heterogeneity and soforth by imparting color, the color heterogeneity and localizeddiscoloration produced by mixing precursors from different lots or bybaking can be prevented and the consistency of product quality can thenbe improved.

The results are shown in Table 3 for investigations in which nozzles forthe arc-extinguishing chamber of a circuit breaker were fabricated fromtetrafluoroethylene resin (PTFE) filled with different insulatingpigments and the wear rate was investigated during the execution ofinterrupt tests. Examples 21 to 24 are examples according to the presentinvention, wherein Example 21 concerns filling with a green insulatingpigment, Examples 22 and 23 concern filling with a blue pigment, andExample 24 concerns filling with a black insulating pigment. ComparativeExample 21 concerns filling with MoS₂, an electroconductive substance;Comparative Example 22 concerns filling with alumina Al₂O₃; ComparativeExample 23 concerns filling with a very small amount (3%) of boronnitride (BN); and Comparative Example 24 concerns the unfilledtetrafluoroethylene resin (PTFE). The “wear rate” was determined bydividing the loss in the nozzle throat diameter and the loss in weightby the introduced energy and is reported as the relative value where“100” is the wear rate for filling with boron nitride BN, which is thesubject of Comparative Example 23.

TABLE 3 filling rate wear rate filler color (weight %) diameter weightExample 21 TiO₂—CoO—NiO—ZnO green 0.60 120 100 Example 22CoO—Al₂O₃—Cr₂O₃ blue 0.60 120 100 Example 23 CoO—Al₂O₃ blue 0.60 160 110Example 24 CuO—Cr₂O₃ black 0.17 210 230 Comparative MoS₂ <0.2 300 370Example 21 Comparative Al₂O₃ 7 120 100 Example 22 Comparative BN 3 100100 Example 23 Comparative none 0 60 110 Example 24

As is clear from Table 3, when the wear rates are compared, the wearrate for the nozzle throat diameter and the weight wear rate are bothsubstantially lower in Examples 21 to 24 than in Comparative Example 21,in which filling is carried out with the electrically conductivematerial, MoS₂. In particular, the weight wear rate in Examples 21 to 23is reduced to the same level as in Comparative Example 23, whichconcerns filling with a very small amount (3%) of BN, and ComparativeExample 24 (no filling).

The results of an investigation are shown in Table into the absorbancearea in the 400 to 700 nm wavelength region for the Examples 21 to 24shown in Table 3. The relationships between the absorbance area at 500to 550 nm and the wear rates (relative value if 100 is used as the valuein Comparative Example 23) for the Examples 21 to 24 shown in Tables 3and 4 are shown graphically in FIGS. 5 and 6. The light absorptionspectra for Examples 21 to 24 and the light reflection spectra forExamples 21 to 24 are shown in FIGS. 7 and 8, respectively. Theabsorbance area values that are the subject of FIGS. 5 and 6 are derivedbased on the light absorption spectra shown in FIG. 7.

TABLE 4 absorbance area wave- wave- wave- wave- wave- wave- wave- lengthlength length length length length length region region region regionregion region region (nm) (nm) (nm) (nm) (nm) (nm) (nm) 400 to 450 to500 to 550 to 600 to 650 to 400 to filler 450 500 550 600 650 700 700Example 21 TiO₂—CoO—NiO—ZnO 48 31 21 34 46 48 228 Example 22CoO—Al₂O₃—Cr₂O₃ 23 20 30 55 59 34 221 Example 23 CoO—Al₂O₃ 12 13 34 5553 19 185 Example 24 CuO—Cr₂O₃ 41 42 44 45 47 48 267

As is clear from Table 4 and FIGS. 5 and 6, a fixed relationship existsbetween the wear rate and the absorbance area. On the other hand, asshown in FIG. 7, the difference in absorbance in the 400 to 450 nmwavelength range is found to have almost no influenced on the wear rate.Accordingly, by carrying out an evaluation of the wear rate for fillingwith different insulating pigments at different filling rates and anevaluation of the absorbance area taking into consideration thewavelength region or regions that have no influence on the wear rate, itis possible to optimize the hue (absorption wavelength) of the pigmentto be introduced and the color density (filling rate).

1. A highly arc-resistant insulator that is disposed and used in a vicinity of arcing that is generated between electrodes, the insulator comprising: a prescribed fluororesin filled with 0.5 to 1 weight % of a non-black insulating pigment that has a heat resistance such that discoloration does not occur when the fluororesin is baked, wherein the fluororesin is a polytetrafluoroethylene resin, and wherein the non-black insulating pigment is a pigment whose main component is a CoO—Al₂O₃—Cr₂O₃ system blue insulating pigment, and wherein a hue (absorption wavelength) and a color density (filling rate) of the insulating pigment are optimized as a result of carrying out an evaluation of a wear rate for different insulators which are filled with different insulating pigments at different filling rates, and an evaluation of an absorbance area thereof taking into consideration a wavelength region or regions that have no influence on the wear rate.
 2. A highly arc-resistant insulator that is disposed and used in a vicinity of arcing that is generated between electrodes, the insulator comprising: a prescribed fluororesin filled with 0.5 to 1 weight % of a non-black insulating pigment that has a heat resistance such that discoloration does not occur when the fluororesin is baked, wherein the fluororesin is a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and wherein the non-black insulating pigment is a pigment whose main component is one or a combination of a TiO₂—CoO—NiO—ZnO system green insulating pigment and a CoO—Al₂O₃—Cr₂O₃ system blue insulating pigment, and wherein a hue (absorption wavelength) and a color density (filling rate) of the insulating pigment are optimized as a result of carrying out an evaluation of a wear rate for different insulators which are filled with different insulating pigments at different filling rates, and an evaluation of an absorbance area thereof taking into consideration a wavelength region or regions that have no influence on the wear rate.
 3. A highly arc-resistant insulator that is disposed and used in a vicinity of arcing that is generated between electrodes, the insulator comprising: a prescribed fluororesin filled with 0.05 to 0.2 weight % of a black insulating pigment that has a heat resistance such that discoloration does not occur when the fluororesin is baked, wherein the fluororesin is a polytetrafluoroethylene resin or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, and wherein the black insulating pigment is a pigment whose main component is one or more selected from the group of a CuO—Cr₂O₃ system, a CoO—Cr₂O₃—Mn₂O₃ system, a CoO—Fe₂O₃—Cr₂O₃ system, and a CuO—Fe₂O₃—Mn₂O₃ system.
 4. The highly arc-resistant insulator according to claim 1, wherein the average particle size of the insulating pigment is 0.4 to 2 μm.
 5. The highly arc-resistant insulator according to claim 2, wherein the average particle size of the insulating pigment is 0.4 to 2 μm.
 6. The highly arc-resistant insulator according to claim 3, wherein the average particle size of the insulating pigment is 0.4 to 2 μm. 